The rebel leader of South Sudan said Monday he would negotiate with South Sudan President Salva Kiir to end the conflict if Kiir released political prisoners.

Rebel leader Reik Machar told Reuters that he would start peace talks with Kiir after nine days of violence if his political allies were released. Donald Booth, the U.S. special envoy to South Sudan, said that Kiir would start talks with Machar to end the fighting.

But Information Minister Michael Makeui said Kiir’s regime was unlikely to release anybody who was accused of planning a coup against him, Reuters reports. Machar was vice president of South Sudan until he was ousted in July amid rumors that he was planning an uprising against Kiir.

Hundreds of people have been killed in the fighting since Dec. 15, and experts say that some of the violence between the government and the rebels has become ethnically based, as Kiir is from the Dinka tribe and Machar is from the Nuer tribe.

Machar told Reuters he had spoken to U.S. National Security Advisor Susan Rice and U.N. envoy Hilde Johnson. “My message was let Salva Kiir release my comrades who are under detention and let them be evacuated to Addis Ababa and we can start dialogue straightaway, because these are the people who would [handle] dialogue,” he said.

The African Union has called for peace over the Christmas holiday.

Meanwhile, two unnamed U.S. military officials told CNN that 150 Marines are preparing to enter South Sudan to help evacuate Americans and protect the U.S. Embassy.